The present invention relates to a rotary separator. More particularly, this invention concerns an apparatus used for separating light and heavy fractions of particulate material.
A separator is known having an upright generally cylindrical housing in the upper portion of which is provided a centered cylindrical sleeve spaced above a frustoconical funnel. The lower end of the funnel is formed as a heavy-fraction outlet and the annular space between the outside of the funnel and the housing is provided with light-fraction outlets. The particulate material is introduced into the upper portion of the housing through a vertically extending tube and falls onto an impingement or distributing plate which axially blocks the end of the inlet tube. Above the sleeve there is provided a fan rotatable about a vertical axis to circulate air or another gas within the housing in a closed path that rises through the sleeve and descends in the annular passage surrounding the sleeve.
When ungraded particulate material is introduced the filler tube into the upper compartment it is first deflected outwardly into the rising air stream in the sleeve. The heavy fraction falls down in the sleeve into the funnel and can be removed. The light fraction is, however, entrained by the rising air and passed up and over the upper edge of the sleeve so as to fall down into the annular space between the funnel and the compartment.
A difficulty with such a separator, particularly when used to separate fines from coal, is that the light fraction adheres and cakes to the inside of the housing, particularly in the upper portion of this housing. In the grading of coal these fines are frequently rather moist so that they can form a rock-hard crust inside the separator. As this crust builds up it reduces the flow cross-section of the annular passage surrounding the sleeve so as to reduce the efficiency of the separator progressively. Eventually this passage will be blocked off altogether and the separator will not function at all.
Thus it is common practice with such a device to shut it down periodically, remove the top of the housing, and scrape off the caked-on lighter fraction. This is an onerous and time-consuming operation. Furthermore, the down-time implicit in such a cleaning operation will reduce the plant efficiency.
I have considered the idea of hanging from the upper wall of the housing a skirt of flexible material spaced slightly inwardly from the housing. Such an arrangement lessens the build-up of light particulate material, as the circulating air keeps the skirt in motion, so that caking-up is unlikely. The disadvantage of this system is that eventually the particulate material cakes to the wall of the housing behind the skirt, eventually completely filling the space between the skirt and the housing and making the skirt completely rigid. Once this occurs the caking-up then continues as in the prior-art arrangements.